Numerical investigation into the thermal interference of slinky ground heat exchangers

Abstract

The thermal performance of a slinky ground heat exchanger has been investigated using a validated transient 3D model for different trench separations, installation depths, soil properties, and daily operation hours. The effect of trench separation on thermal interference was analysed. The centre-to-centre distances between parallel trenches range from 1.5 m to 11 m. The initial soil temperature was found to have a significant effect on the predicted thermal performance. The predicted heat extraction using a varying initial soil temperature for a heating season would decrease with the increasing depth of installation, whereas using a uniform initial temperature would lead to increasing heat extraction with installation depth. It has also been found that soil with a high thermal conductivity would exacerbate the thermal interference between trenches with a small separation and that the thermal interference in continuous operation would be more than that in intermittent operation as a result of heat depletion in the ground. The effect of installation depth depended on the initial soil temperature for the first three months of continuous operation, but the effect decreased with operating time.